Double container



TEAR STRENGTH Dec. 21, 1965 A. N. SPANEL DOUBLE CONTAINER Filed FebMANUALLY BURSTA BL E B MIN. B/MAX.

1 SAFE FROM BURSTING FROM SHIPPING OR HANDLING BURST STRENGTH FIG.4.

INVENTOR Abraham N. Sponel www ATTORNEY United States Patent 3,224,570DOUBLE CONTAINER Abraham N. Spanel, Princeton, NJ, assignor toInternational Latex Corporation, Dover, Del, a corporation oi DelawareFiled Feb. 14, 1961, Ser. No. 89,256 5 Claims. (Cl. 206-47) Thisinvention relates to double containers in which a smaller innercontainer is adapted to be burst without bursting the larger outercontainer, so that when desired the contents of the inner container maybe mixed with the contents of the intact outer container.

One instance of a product of this type, in which the article should besoftly flexible to fit the human face or various contours to which itmay be applied, is the refrigerating package shown in Patent No.2,925,719 to Robbins et al. It has an inner sealed envelope filled withwater. An outer sealed envelope contains both the inner envelope and awater-soluble chemical which has an endothermic heat of solution. Theenvelopes are flexible plastic and when the package is squeezed theinner envelope breaks and the Water contacts the chemical. The heat ofsolution is absorbed and the package becomes a cold pack.

Tlhese refrigerating packages are often to be used under emergencyconditions, for example to hold down swelling due to injury, wherein theuser may not be familiar with the design and functioning of the productand may be hurried or even distraught. If the product is so designedthat when it is squeezed the inner container will rupture locally, witha limited break in just one part of the inner envelope, then only alimited quantity of the water from the inner conainer may come intocontact with the chemical and the rest may remain inside the innercontainer. This leaves appreciable quantities of the salt undissolved,and only a part of the cooling capacity of the package is realized.Under likely conditions of application the user may neither sense thisdeficiency nor take the time to resort to such kneading or turning asmight serve to discharge all the water from the inner container.

The present invention assures that when the inner container is broken atall it will split wide open and let out all the water to produce maximumcoldness.

I attain this result by making the outer envelope of stretchable plasticfilm arid the inner envelope of nonstretchable plastic film having thecombination of a moderately high bursting strength and a very low tearstrength, that is, a high tear propagation characteristic. When such anenvelope filled with water is squeezed to burst it, the relatively highpressure present at the moment of initial rupture will propagate animmediate tear that splits the envelope wide open. The reason that thetear propagation characteristic must be very high is that upon initialrupture some of the water or residual air escapes and drops the pressurealmost instantaneously (unless the person squeezing the bag makes arather extraordinary effort to press harder when the container begins togive). This, it is necessary for the purpose of this invention to makethe inner container of material which will tear across an entire face ofthe envelope while the pressure is rapidly dropping to zero. While ahigher burst strength would permit of a higher tear strength, the burststrength must in practice be well within the range of manual squeezingforce, so the purpose of the invention can only be attained by combiningwith that moderately high bursting strength a very high tear propagationcharacteristic.

The drawings illustrate a package of the sort this invention isapplicable to.

Patented Dec. 21, 1965 FIGURE 1 shows a double package 15, having innerenvelope 10 filled or largely filled with water 12, and endothermicchemical 14 also contained in the outer envel'ope 16.

FIGURES 2 and 3 show for simplicity only the inner container.

FIGURE 2 illustrates an inner container made of relatively stretchablernaterial having a low tear propagation characteristic so that whenburst by application of pressure above its bursting strength only aslight break is created in the wall of the envelope and much of thewater is held in the envelope when maintained in the position shown.

FIGURE 3 illustrates an inner envelope of the type used in the presentinvention which has a tear strength equal to or less than the burstingstrength of the relatively non-stretchable plastic and a high tearpropagation characteristic so that application of bursting pressurecauses substantially complete splitting of the material across at leastone face of the envelope.

FIGURE 4 is a graphic representation of the coordinated burst strengthand tear strength characteristics of the inner envelope of the doublecontainer of the invention.

In FIGURE 4, no exact values are assigned to B which is the minimumacceptable burst strength of the material of the inner envelope, and Bwhich is the maximum acceptable, for the reason that these may varysomewhat depending upon the size and shape of the envelope. Theacceptable range of values for a representative size and shape ofenvelope is about 30 p.s.i. to about 60 psi. on the Mullen Burst Test,which reads in pounds per square inch. No novelty is claimed in theseburst strength values by themselves, the novelty lying in thecombination of this general range of moderately high burst strengthtogether with a corresponding very low tear strength and acorrespondingly high tear propagation characteristic.

I have found that materials with burst strengths all in the range of 30to 60 psi. have tear strengths which differ widely, some being a hundredtimes as resistant to tear as others with the same burst strength. Thisis with a test procedure wherein a portion of the top edge of a samplestrip of sheet plastic material is clamped to hold it, a clamp isattached next to that portion, with a weight suspended from it, and astandard short slit is cut in the top edge between the two clamps. Theweight necessary to cause the sample to tear apart as a continuation ofthe slit is recorded as the tear strength. In the test equipment used,the free clamp weighed 8 grams, so values below 8 grams were notdistinguishable. Values were recorded from as high 800 grams down to 8grams (or lower).

The fundamental concept of the invention is the selection and use of amaterial having the requisite moderately high burst strength and at thesame time a corresponding very low tear strength for the inner envelope,while the outer envelope is resistant to rupture when hand manipulatedto produce the required pressure to burst the inner envelope. The outerenvelope is desirably made of an elastomer-like material, which amongothers may be polyethylene or vinyl-type resins. The boundaries may beidentified empirically as a burst strength (in relation to the size andshape of the filled inner envelope) high enough not to burst in shippingand handling and low enough to be manually burstable, and a tearstrength low enough so that an initial rupture will propagate the tearto split the envelope wide open during the almost instantaneous periodwhen the pressure is dropping from bursting pressure to zero. In termsof scale values they may be identified as any satisfactory burststrength including and lying in the general vicinity of 30 to 60 p.s.i.,and a tear strength (after initiation of rupture) of not more than aboutthe same value in grams, to wit a maximum of not more than about 60grams, ranging down toward zero. The higher the burst strength, thehigher the tear strength may be. The upper limit of the tear strength ingrams has the same numerical value as the selected burst strength, inpounds per square inch.

This combination is found in cellophane about 1.5 mils in thickness, itsburst strength being 50 to 60 p.s.i. and its tear strength being wellwithin that upper limit, namely, 8 grams or less. When greaterwaterproof quality is desired, an inner layer of suitable highlywaterproof plastic film may be laminated to the cellophane, as indicatedat 1011 and 10b in FIGURE 3. The inner layer may be of material which,if thicker and used as the only layer, would have too high a tearstrength, provided the outer layer is unstretchable and the compositematerial is kept within the combination of characteristics set forthabove.

The result is a product which serves the intended purpose effectivelyand by its very constituency guards against the partial ineffectivenesswhich with other constituencies can often in large measure defeat theintended purpose of the product.

Having described the nature of my invention and indicated how it can bepracticed,

I claim:

1. Container comprising an outer larger pliable envelope of one burstingstrength containing a water soluble chemical having an endothermic heatof solution and an inner smaller water-filled pliable envelope ofbursting strength less than that of the outer envelope, the innerenvelope being made of plastic film having a Mullen burst strength ofabout 30 to 60 p.s.i. and having a tear strength in grams measured asherein described, the upper limit of tear strength in grams having thesame numerical value as the burst strength in p.s.i.

2. A container according to claim 1 in which the plastic film of theinner envelope is cellophane.

3. In a double envelope package having an inner sealed envelopesubstantially filled with liquid, an outer sealed envelope containingthe inner envelope and a substance adapted to be mixed with said liquidupon bursting of the inner envelope upon application of force to theouter envelope, said outer envelope having a higher bursting strengththan said inner envelope, the improvement comprising said inner envelopeconstructed of sheet plastic having a tear strength, the upper limit ofwhich expressed in grams has the same numerical value as the burststrength expressed in p.s.i., such that the envelope splits open atleast on one face thereof upon application of bursting pressure theretowhereby to substantially instantly completely discharge the liquid fromthe inner envelope upon subjecting the same to bursting pressure.

4. A device as claimed in claim 3, in which the inner envelope is madeat least in part of substantially unstretchable sheet plastic.

5. A device as claimed in claim 3 in which the inner envelope is atwo-ply laminate of plastic material, the inner ply being of highlywaterproof plastic and the outer ply being of less waterproof butsubstantially unstretchable plastic.

References Cited by the Examiner UNITED STATES PATENTS 2,209,914 7/1940Gerber et al. 20656 2,923,404 2/ 1960 Adell 20656 2,925,719 2/1960Robbins 624 2,971,850 2/1961 Barton 20647 X JOSEPH R. LECLAIR, PrimaryExaminer.

EARLE J. DRUMMOND, FRANKLIN T. GARRETT,

Examiners.

1. CONTAINER COMPRISING AN OUTER LARGER PLIABLE ENVELOPE OF ONE BURSTINGSTRENGTH CONTAINING A WATER SOLUBLE CHEMICAL HAVING AN ENDOTHERMIC HEATOF SOLUTION AND AN INNER SMALLER WATER-FILLED PLIABLE ENVELOPE OFBURSTING STRENGTH LESS THAN THAT OF THE OUTER ENVELOPE, THE INNERENVELOPE BEING MADE OF PLASTIC FILM HAVING A MULLEN BURST STRENGTH OFABOUT 30 TO 60 P.S.I. AND HAVING A TEAR STRENGTH IN GRAMS MEASURED ASHEREIN DESCRIBED, THE UPPER LIMIT OF TEAR STRENGTH IN GRAMS HAVING THESAME NUMERICAL VALUE AS THE BURST STRENGTH IN P.S.I.